JPH0318163B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an exposure control device for a microscopic photographing device, and more particularly to an exposure control device that uses a photomultiplier tube as a photoelectric conversion element for photometry and determines a shutter speed based on a photoelectric conversion signal of the photomultiplier tube. 2. Description of the Related Art In recent years, exposure control devices have been developed for microscopic photography devices, similar to still cameras, that photoelectrically convert light from an objective lens and automatically determine shutter speed based on this photoelectric conversion signal. The light from a microscope specimen varies widely, from very dark to quite bright, so if you want to automatically photograph such specimens, you need a photoelectric conversion element that has photometric sensitivity over an extremely wide range. You need to choose. Since a small semiconductor photoelectric conversion element such as a photocell is not sensitive to very dim light such as that of a fluorescent specimen, the use of a photomultiplier tube is considered. However, a photomultiplier tube that has a wide photometric range that covers from very dark light to fairly bright light is large and expensive, and therefore is not suitable as a light receiving device for a microphotographing device. Therefore, it is sufficient to use a small photomultiplier tube, but in order to cover a wide photometric area, it is necessary to make the sensitivity variable. It is necessary to cover a wide photometric area. Conventionally, the sensitivity setting of such a small photomultiplier tube has been done manually, for example, as used in a photometer. However, an automated microscope photography device is desired. An object of the present invention is to provide an exposure control device that automates the sensitivity setting of the photomultiplier tube in a microscopic photographing apparatus using a photomultiplier tube as a photometric element. The exposure control device of the present invention is configured to automatically switch the sensitivity of a photomultiplier tube and to automatically correct exposure in conjunction with the switching of the sensitivity. The present invention will be described below based on embodiments shown in the drawings. There are applied voltage and detection resistance as elements that give the sensitivity of a photomultiplier tube. In this example, two types of applied voltage (high resistance) and two types of detection resistance (high and low) were prepared in order to change the sensitivity stepwise. Three levels of sensitivity were set by combining high voltage-low resistance, low voltage-high resistance, and low voltage-low resistance. In FIG. 1, a high voltage source 2 and a low voltage source 3 can be selectively applied to a photomultiplier tube 1 via a changeover switch SW1. The output of the photomultiplier tube 1 is input to a preamplifier 4 with a large detection resistor and a preamplifier 5 with a small detection resistor. The preamplifiers 4 and 5 are
It is selectively connected to the logarithmic conversion circuit 6 via the changeover switch SW2. The output of the logarithmic conversion circuit 6 is input to the exposure calculation circuit 7 and also to the first and second comparison circuits 8 and 9. The first comparator circuit 8 is supplied with a voltage V _H that determines the over limit from the battery 8a, and this voltage V _H and the logarithmic conversion circuit 6
If the latter is larger than the former, a low level signal L is output, and otherwise a high level signal H is output. A light emitting element 8b is connected to the output terminal of the first comparing circuit 8, and this light emitting element 8b lights up when the output of the first comparing circuit 8 is a low level signal. On the other hand, the second comparator circuit 9 is given a voltage V _L that determines the under limit from the battery 9a, and compares this voltage V _L with the output of the logarithmic conversion circuit 6, and if the latter is smaller than the former, it is determined that the voltage is low. At other times, a high level signal H is output. A light emitting element 9b is connected to the output terminal of the second comparison circuit 9, and this light emitting element 9b lights up when the output of the second comparison circuit 9 is a low level signal. The control signal generation circuit 10 inputs the outputs of the first and second comparison circuits 8 and 9, and selects one of the first, second, and third output terminals 10a, 10b, and 10c depending on the level of the output level. Outputs a high level signal to the The first, second, and third output terminals 10a, 10b, and 10c are connected to a first switch control circuit 11. The first switch control circuit 11 has first, second, and third output terminals 10a, 10
Switch SW3, SW4, SW depending on which high level signal is output to
A signal is generated to turn on the corresponding switch among the switches. One ends of the switches SW3, SW4, and SW5 are connected to first, second, and
It is connected to the third correction coefficient output circuits 12a, 12b, and 12c, and the other end is connected to the dew insect calculation circuit 7. The control signal generation circuit 10 also determines the high and low levels related to the output signals of the first, second, and third output terminals 10a, 10b, and 10c in accordance with the high and low levels of the output levels of the first and second comparison circuits 8 and 9. The combined signals are output to the fourth and fifth output terminals 10d and 10e. The fourth and fifth output terminals 10d and 10e are connected to a second switch switching circuit 13. The second switch switching circuit 13 operates the switching switch according to the relationship shown in Table 1 according to the combination of the output terminals 10d and 10e.
Switch SW1 and SW2.

[Table] The exposure calculation circuit 7 receives the photometric value from the logarithmic conversion circuit 6, the first, second, and third correction coefficient output circuits 12a,
The exposure time is calculated and output from the correction coefficient from either one of 12b and 12c and the film sensitivity from the film sensitivity setting device 14. The output of the exposure calculation circuit 7 is displayed on the display circuit 15 and is also input to the shutter control circuit 16. Next, details of the conversion circuit 10 will be explained using FIG. 2. The first code conversion circuit 100 has first, second, and third input terminals a, b, and c, and first and second output terminals d and e. The output of the first comparator circuit 8 is input to the first input terminal a of the first code conversion circuit 100, the first output terminal d is input to the second input terminal b, and the second output is input to the third input terminal c. Terminals e are connected to each other. The first code conversion circuit 100 converts three combinations of high-level signals H and low-level signals L input to terminals a, b, and c.
Bit input code, and 2 corresponding to the code.
The combination of bit output signals (output code) is converted according to the relationship shown in Table 2 and output to terminals d and e. Such a code conversion circuit can be easily designed using well-known technology. For example, a 3-bit input code is used as address designation data, and 2 bits are sent to the corresponding address.
A readable memory having a bit output code can be used.

[Table] The second code conversion circuit 101 also has the first, second,
It has a third input terminal, a', b', c', and first and second outputs d', e'. Second code conversion circuit 101
The output of the second comparator circuit 9 is input to the first input terminal a', and the first output terminal is input to the second input terminal b'.
d′ is connected to the third input terminal c′, and the second output terminal is connected to the third input terminal c′.
e′ are connected to each other. The second code conversion circuit 101 uses the combination of the high level signal H and the low level signal L input to the terminals a', b', and c' as a 3-bit input code, and converts the 3-bit input code into Combination of bit output signals (output code)
is converted according to the relationship shown in Table 3 and output to terminals d' and e'.

[Table] The multiplexer 102 has a control terminal 102a, and depending on the H and L signals input to the control terminal 102a, it converts the output of the first code conversion circuit 100 when the signal is L and converts the second code when the signal is H. The outputs of the circuits 101 are respectively input to a third code conversion circuit 104. Set, reset flip-flop 103
The output of the first comparator circuit 8 is input to the reset terminal R, and the output of the second comparator circuit 9 is input to the set terminal S via the inverter In1. Conversely, the flip-flop 103 is reset to output the output of the first code conversion circuit 100 when the output of the first comparison circuit 8 is L, and is set to output the output of the first code conversion circuit 100 when the output of the second comparison circuit 9 is L. The output of the 2-code conversion circuit 101 is
The multiplexer 102 is controlled so that the multiplexer 102 passes. The third code conversion circuit 104 converts the output code of the first code conversion circuit 100 or the second code conversion circuit 101 that has passed through the multiplexer 102 into a 3-bit code according to the relationship shown in Table 4, and outputs the code.

[Table] The output of the third code conversion circuit 104 is input to the fourth code conversion circuit 105, and is also output from the control signal generation circuit 10 via terminals 10a, 10b, and 10c, and is also input to the switch control circuit 11. . The fourth code conversion circuit 105 receives the input 3
The bit code is converted into a 2-bit code by reversing the input and output in Table 4 and output. Fourth
The output of the code conversion circuit 105 is outputted from the control signal generation circuit 10 via terminals 10d and 10e and inputted to the second switch control circuit 13 to switch the changeover switches SW1 and SW2. Next, the operation of the circuit will be explained with reference to FIG. First, it is assumed that the first changeover switch SW1 is connected to the terminal q, the second changeover switch SW2 is connected to the terminal q', and the sensitivity of the photomultiplier tube 1 is set to the lowest. In this case, from Table 1,
Output terminals 10d and 10e of control signal generation circuit 10
outputs L, respectively, and the output terminals 10a,
It can be seen from Table 4 that 10b and 10c sequentially output HLL. Therefore, the changeover switch SW
3 is on, and the exposure calculation circuit 7 is connected to the first correction coefficient output circuit 12a. In such a state, the output of the logarithmic conversion circuit 6 is as shown in FIG.
If V _a is considerably smaller than the voltage V _L of the second comparison circuit 9, the output of the first comparison circuit 8 will be H, and the output of the second comparison circuit 9 will be L. Therefore,
The light emitting element 9b lights up to warn that the output of the logarithmic conversion circuit 6 is smaller than the under limit _VL . In this case, flip-flop 103 is set and the output code of second code conversion circuit 101 passes through multiplexer 102. If the output code of the second code conversion circuit 101 is LL, the output of the control signal generation circuit 10 remains unchanged. At this time,
Input terminals a', b' of the second code conversion circuit 101,
Since c' becomes LLL sequentially, from Table 3, its output terminal
The code output to d' and e' is HL. As a result, the third code conversion circuit 104 outputs the code LHL from Table 4, and the first switch control circuit 11 turns off the switch SW3 and turns on the switch SW4. Further, the fourth code conversion circuit 105 converts the code into
outputs HL and therefore the second switch control circuit 13
According to the relationship in Table 1, selector switch SW2 is connected to terminal
Switch to p′. As a result, the sensitivity increases by one level, and the output of the logarithmic conversion circuit 6 increases to V _b in FIG. 3. In addition, in FIG. 3, it is necessary that V _H −V _L >V _b −V _a . However, in this case as well, the second comparison circuit 9
Since the output of is L, the second code conversion circuit 10
1 is sequentially applied to output terminals d' and e' according to the relationship in Table 3.
Outputs LH (i.e. output code LH). Then, the third code conversion circuit 104 outputs the code LLH according to the relationship shown in Table 4, so the first switch switching circuit 11 turns off the changeover switch SW4 and turns on the switch SW5. Further, since the fourth code conversion circuit 105 outputs the code LH according to the relationship shown in Table 4, the second switch switching circuit 13 switches the switch SW1 to the terminal p according to the relationship shown in Table 1. By doing so, the sensitivity is further increased by one step, and if the output of the logarithmic conversion circuit ₆ becomes as shown in FIG. , flip-flop 103
does not change its state, so the control signal generation circuit 10 is in a stable state. Furthermore, preferably V _b
−V _a =V _c −V _b and at least V _H −V _L >V _c −
Must be V _b . Otherwise, the output of the logarithmic conversion circuit 6 would fluctuate between the under limit V _H and the over limit V _L due to sensitivity switching. The arithmetic circuit 7 receives the correction coefficient from the third correction coefficient output circuit 12c and the logarithmic conversion circuit 6.
An appropriate exposure time is calculated from the output from the film sensitivity setting device 14 and the film sensitivity from the film sensitivity setting device 14, and is displayed on the display circuit 15. That is, the photographer uses the light emitting elements 8b and 9b.
By reading the display on the display circuit 15 when the light is off, the appropriate exposure time can be determined. When a release button (not shown) is turned on, the shutter control circuit 16 is opened for the proper exposure time. Although it is clear from the above explanation, in other words, the output terminal d' of the second code conversion circuit 101,
The code output to e' is configured so that the operation of changing to a new code occurs after the time required to complete the circuit settings (sensitivity settings, correction coefficient settings, etc.) corresponding to the changed code. has been done. Further, the same applies to the first code conversion circuit 100. Next, if the incident light increases and the output of the logarithmic conversion circuit 6 increases, as shown in _FIG . It is. Therefore, the light emitting element 8b lights up, indicating that the output of the logarithmic conversion circuit 6 is greater than the over limit _VH . At this time, the control signal generation circuit 10
Since the flip-flop 103 inside is reset, the multiplexer 102 is connected to the first code conversion circuit 1.
Pass the output of 00. First code conversion circuit 1
If the output code of 00 is LL, the output code of the fourth code conversion circuit 100 is also LL, switch SW1 is connected to terminal q, and switch SW2 is connected to terminal q.
q', and the output of the logarithmic conversion circuit 6 becomes as shown in FIG. 3, V _f . Of course, the first code conversion circuit 1
If the output code of 00 is LH, the output code is switched to HL in the first stage, and after the output of the logarithmic conversion circuit 6 becomes V _d , the first code conversion circuit 100
The output code of becomes LL, and the output of the logarithmic conversion circuit 6 becomes V _f as described above. The size of the incident light and
Although the circuit operation will differ depending on the setting sensitivity,
Since it is self-evident from the above description, it will not be necessary to explain the circuit operation for all possibilities. Of course, even if the incident light to the photomultiplier tube 1 is extremely small and the sensitivity of the photomultiplier tube 1 is at its highest, the output of the logarithmic conversion circuit 6 falls below the under limit V _L , the light emitting element 9b will light up. Next, it warns the photographer that the subject is too dark and automatic exposure is not possible, and also warns the photographer that when the incident light on the photomultiplier tube 1 is extremely large, even if the sensitivity of the photomultiplier tube 1 is at its minimum. When the output of the logarithmic conversion circuit 6 exceeds the over-limit, the light emitting element 8b continues to light up to warn the photographer that the subject is too bright and automatic exposure is impossible. In the latter case, if the dynode or anode of the photomultiplier tube 1 may be damaged if left as is for a long time, for example, the code LL of the output terminals 10d and 10e of the control signal generation circuit 10 It would be convenient if an AND signal with the output L of the first comparator circuit 8 was used to automatically insert an ND filter into the optical path, or to activate a protection circuit for the photomultiplier tube 1. . Also, if the linearity range of the circuit that processes the output of the photomultiplier tube is narrow, overlimiting may occur.
This can be done by narrowing the widths of V _H and under-limit V _L. As described above, according to the present invention, the sensitivity of the photomultiplier tube is automatically changed and the exposure is automatically corrected in conjunction with the sensitivity change, so that the exposure control is compact, easy to operate, and has a wide photometry range. You can get the equipment. Further, by keeping the output of the photomultiplier tube within a predetermined range, there is no need to widen the dynamic range of a processing circuit such as a logarithmic conversion circuit, and the degree of freedom in circuit design increases.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing one embodiment of the device of the present invention, Fig. 2 is a circuit diagram showing details of the conversion circuit of the device shown in Fig. 1, and Fig. 3 explains the operation of the circuit of the present invention. An explanatory diagram for Explanation of symbols of main parts, photomultiplier tube...1,
Means for changing the sensitivity of a photomultiplier tube...2, 3,
SW1, signal generation means...10, correction coefficient output means...12a, 12b, 12c.

Claims (1)

[Scope of Claims] 1. An exposure control device in a photographing device for a microscope, which is configured such that a light flux from an objective lens is photoelectrically converted by a photometric element, and an exposure calculation means automatically determines a shutter speed based on the photoelectric conversion signal. A photomultiplier tube as the photometric element, and a level of the photoelectric conversion signal obtained from the photomultiplier tube is compared with a predetermined level range, so that the level of the photoelectric conversion signal is set to the predetermined level. a comparison means for detecting whether the level of the photoelectric conversion signal is within the range and outputting a detection signal; a sensitivity control means for changing the sensitivity of the photomultiplier tube stepwise so that the sensitivity falls within the predetermined level range; and a correction value according to the sensitivity of the photomultiplier tube, correction value output means controlled by a signal to output a correction value according to the sensitivity of the photomultiplier tube to the exposure calculation means, the exposure calculation means adding the correction value to the photoelectric conversion signal. An exposure control device characterized in that the exposure control device determines a shutter speed.